Incidental focal ¹⁸F-FDG uptake on the spinal cord in patients with cancer: prevalence and risk of malignancy

Objectives When focal ¹⁸F-FDG uptake on the spinal cord is incidentally found, its’ clinical significance is not established well. We investigated the incidence, location, and clinical significance of that uptake in patients with cancer.

Methods The subjects were 23,355 patients with known or suspicious malignancy who underwent ¹⁸F-FDG PET/CT between from Jan 2013 to May 2014. By medical records review, PET/CT with incidental focal spinal cord uptake were selected and retrospectively reviewed to determine the presence, location, number and maximum standardized uptake value of focal hypermetabolic lesion on spinal cords. In subjects with focal spinal uptake, characteristics and clinical follow-up results including follow-up PET/CT were reviewed.

Results Incidental focal spinal cord uptake was observed in 101 of 23,355 patients (0.43%). Among them, 25 patients who had prior history of radiation therapy to spinal cord or organs adjacent to spinal cord, or spinal cord malignancy were excluded from further analysis. 76 patients (M:F = 37:39; age, 51.1 ± 20.5 years) were finally included. Most common site with focal spinal cord uptake was the cord at the level of 12^th thoracic vertebra (45/76; 59%). Second common site was the cord at the level of 1st lumbar vertebra (13/76; 17%). Multifocal uptake was found in 9 of the 76 patients (11.8%). The average SUVmax of those cord uptakes was 2.5 ± 0.6 (range, 1.4~3.9). In all 46 patients with clinical follow-up for more than 6 months, there was no evidence of abnormalities on the spinal cords both at the time of PET/CT and during clinical follow-up. Of the 16 patients with follow-up PET/CT (3-12 m months after prior PET/CT), those focal spinal cord uptakes were disappeared in 9 (56.3%) and, were stationary or reduced In the remaining 7 patients (43.7%),

Conclusions Although incidental focal ¹⁸F-FDG uptake on spinal cords in patients with cancer is rare, it may be physiological or benign, which should not be considered as malignant involvement. Common sites of those uptakes are spinal cords at the levels of T12-L1 spines.